@DaveTweed removing incorrect comments does not constitute an apology.

So do you still think that differentiation is "useless in practice" @DaveTweed, or have done a little review of first year and realized that it applies to, oh, one or two aspects of DSP?

I'm getting a bit sick of being targeted, and I'm not pleased about having my downvotes reversed. How I choose to spend my reputation is up to me, not whichever puffed up ego decided otherwise.